A cost effective way of fabricating integrated circuit die is to simultaneously form multiple circuits on a single semiconductor wafer and then break the wafer into die. This form of batch processing, or wafer processing, allows the cost of each step of the fabrication process to be spread among many devices and reduces the handling that would be required to process each device individually. A typical process flow includes many lithography, deposition, doping, etching, and testing steps. As the circuits are formed on the wafer, horizontally and vertically extending "streets" are defined in the wafer which extend between and separate the circuits from one another. These streets then may typically be scribed or partially sawn process to form kerfs. The wafer can then be broken along these kerfs to form the individual die which can then be packaged with leads.
When a micromechanical wafer is broken to form the individual die, care must be taken so as to minimize the generation of particles, and prevent the die edges from touching. Conventionally, the completed wafer is first placed on a flexible membrane or wafer stretch tape having an adhesive on one side to secure the wafer to the tape. This adhesive tape maintains the individual die in place as the dies are formed during the break process. Care must be taken to prevent the tape from shrinking back to the point where the die edges could touch one another and cause damage. This is especially critical for micromechanical devices having moving parts.
Conventionally, the die formed on a wafer are generally square, or slightly rectangular and thus have a low aspect ratio. That is, the length of the die sides are about equal and the aspect ratio approaches 1:1. These generally square die can thus be separated using many conventional techniques. One such technique is shown in commonly assigned U.S. Pat. No. 3,562,057. A spherical dome can be driven downward against the backside of the wafer to cause the wafer to break along the intersecting kerfs and form individual die. A spherical dome is appropriate when the dies are generally square, that is, having a low aspect ratio. Another similar device is shown in U.S. Pat. No. 5,104,023 whereby a hemispherical body presses a wafer against a resilient rubber mat. Such a device breaks the wafer along the kerfs in both directions from the wafer center outward, that is, such that cracking of the wafer is initiated from a center thereof towards the periphery thereof.
However, such hemispherically shaped domes are unsuitable for separating wafer die that have a high aspect ratio, such as rectangular spatial light modulators used in display systems, and exceptionally elongated die used in printer systems. Such systems incorporating elongated die are shown in commonly assigned U.S. Pat. No. 5,079,544 to DeMond, et al. entitled "Standard Independent Digitized Video System" and U.S. Pat. No. 5,105,369 to Nelson, entitled "Printing System Exposure Module Alignment Method and Apparatus of Manufacture", the teachings of each incorporated herein by reference. The spatial light modulator die used in the display system typically has an aspect ratio of 9:16. The die used in the printer system is comprised of an integrated circuit formed as an exceptionally elongated array of micromirrors, having a length of about 5" and an aspect ratio of 1:25. Due to the extreme length of this die, especially in view of the short width, this die can not be suitably separated from the other dies of a wafer using a spherically shaped dome as the die would fracture in the long direction. A plurality of elongated dies formed on a wafer for displays and printers is shown in FIG. 2(a) and FIG. 2(b), respectively, of the present application.
It is desired to provide a method and apparatus to be used for breaking die having a high aspect ratio, ie. those being rectangular rather than square, without fracturing the die in the long dimension during the breaking process. Such a method and apparatus should reduce the generation of silicon particles during wafer break while preventing the die edges from rubbing with one another during and after the break.